Messages in this thread Patch in this message | | | Date | Tue, 31 Jan 2023 16:10:19 +0100 | Subject | Re: [GIT PULL] iov_iter: Improve page extraction (pin or just list) | From | David Hildenbrand <> |
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On 31.01.23 16:04, Jens Axboe wrote: > On 1/31/23 8:02?AM, David Hildenbrand wrote: >> On 31.01.23 15:50, Jens Axboe wrote: >>> On 1/31/23 6:48?AM, David Hildenbrand wrote: >>>> On 31.01.23 14:41, David Howells wrote: >>>>> David Hildenbrand <david@redhat.com> wrote: >>>>> >>>>>>>> percpu counters maybe - add them up at the point of viewing? >>>>>>> They are percpu, see my last email. But for every 108 changes (on >>>>>>> my system), they will do two atomic_long_adds(). So not very >>>>>>> useful for anything but low frequency modifications. >>>>>>> >>>>>> >>>>>> Can we just treat the whole acquired/released accounting as a debug mechanism >>>>>> to detect missing releases and do it only for debug kernels? >>>>>> >>>>>> >>>>>> The pcpu counter is an s8, so we have to flush on a regular basis and cannot >>>>>> really defer it any longer ... but I'm curious if it would be of any help to >>>>>> only have a single PINNED counter that goes into both directions (inc/dec on >>>>>> pin/release), to reduce the flushing. >>>>>> >>>>>> Of course, once we pin/release more than ~108 pages in one go or we switch >>>>>> CPUs frequently it won't be that much of a help ... >>>>> >>>>> What are the stats actually used for? Is it just debugging, or do we actually >>>>> have users for them (control groups spring to mind)? >>>> >>>> As it's really just "how many pinning events" vs. "how many unpinning >>>> events", I assume it's only for debugging. >>>> >>>> For example, if you pin the same page twice it would not get accounted >>>> as "a single page is pinned". >>> >>> How about something like the below then? I can send it out as a real >>> patch, will run a sanity check on it first but would be surprised if >>> this doesn't fix it. >>> >>> >>> diff --git a/mm/gup.c b/mm/gup.c >>> index f45a3a5be53a..41abb16286ec 100644 >>> --- a/mm/gup.c >>> +++ b/mm/gup.c >>> @@ -168,7 +168,9 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags) >>> */ >>> smp_mb__after_atomic(); >>> +#ifdef CONFIG_DEBUG_VM >>> node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs); >>> +#endif >>> return folio; >>> } >>> @@ -180,7 +182,9 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags) >>> static void gup_put_folio(struct folio *folio, int refs, unsigned int flags) >>> { >>> if (flags & FOLL_PIN) { >>> +#ifdef CONFIG_DEBUG_VM >>> node_stat_mod_folio(folio, NR_FOLL_PIN_RELEASED, refs); >>> +#endif >>> if (folio_test_large(folio)) >>> atomic_sub(refs, folio_pincount_ptr(folio)); >>> else >>> @@ -236,8 +240,9 @@ int __must_check try_grab_page(struct page *page, unsigned int flags) >>> } else { >>> folio_ref_add(folio, GUP_PIN_COUNTING_BIAS); >>> } >>> - >>> +#ifdef CONFIG_DEBUG_VM >>> node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1); >>> +#endif >>> } >>> return 0; >>> >> >> We might want to hide the counters completely by defining them only >> with CONFIG_DEBUG_VM. > > Are all of them debug aids only? If so, yes we should just have > node_stat_* under CONFIG_DEBUG_VM. >
Rather only these 2. Smth like:
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 815c7c2edf45..a526964b65ce 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -196,8 +196,10 @@ enum node_stat_item { NR_WRITTEN, /* page writings since bootup */ NR_THROTTLED_WRITTEN, /* NR_WRITTEN while reclaim throttled */ NR_KERNEL_MISC_RECLAIMABLE, /* reclaimable non-slab kernel pages */ +#ifdef CONFIG_DEBUG_VM NR_FOLL_PIN_ACQUIRED, /* via: pin_user_page(), gup flag: FOLL_PIN */ NR_FOLL_PIN_RELEASED, /* pages returned via unpin_user_page() */ +#endif NR_KERNEL_STACK_KB, /* measured in KiB */ #if IS_ENABLED(CONFIG_SHADOW_CALL_STACK) NR_KERNEL_SCS_KB, /* measured in KiB */ diff --git a/mm/vmstat.c b/mm/vmstat.c index 1ea6a5ce1c41..5cbd9a1924bf 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1227,8 +1227,10 @@ const char * const vmstat_text[] = { "nr_written", "nr_throttled_written", "nr_kernel_misc_reclaimable", +#ifdef CONFIG_DEBUG_VM "nr_foll_pin_acquired", "nr_foll_pin_released", +#endif "nr_kernel_stack", #if IS_ENABLED(CONFIG_SHADOW_CALL_STACK) "nr_shadow_call_stack", -- Thanks,
David / dhildenb
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